We had it professionally installed by Lowe's and I see in the Q&A that a 1/4" plywood is necessary over 3/4" plywood subfloor per the manufacturer, but I know for certain it was installed directly over the subfloor - is that a problem?

Hello a150n and thank you for your inquiry. In order to prevent subfloor weakness and to keep the floor from flexing, the plywood subfloor should be greater than 1" in overall thickness in order to stay within the manufacturer's warranty specifications. If the floor does fail in the future, and it was caused by weakness in the subfloor, the chances of a claim being honored are not good. We always recommend following the manufacturer's Warranty and Installation Guidelines when it comes to installing your new luxury vinyl flooring. Hope this helps. Thanks again for choosing Style Selections Luxury Vinyl Plank.